1. Field of the Invention
The present invention relates to a driving method for a flat panel display device. More particularly, the present invention relates to a pixel driving method which achieves a low colour washout of a liquid crystal display (LCD).
2. Description of Related Art
Since an LCD has such advantages as high image quality, high space utilization efficiency, low power consumption and no radiation etc., it has gradually become popular in the market. Presently, features such as high contrast ratio, fast response and wide viewing angle are general requirements of the LCD in the market. The wide viewing angle may be achieved based on techniques such as multi-domain vertically alignment (MVA), multi-domain horizontal alignment (MHA), twisted nematic plus wide viewing film (TN+film) and in-plane switching (IPS).
FIG. 1 is a schematic diagram illustrating a gamma curve A actually measured based on a large viewing angle of an LCD (hereinafter referred to as side viewing angle gamma curve) and a gamma curve B actually measured based on a direct viewing angle of the LCD (hereinafter referred to as direct viewing angle gamma curve). Pixel resolution of the LCD is 8 bits (i.e. 0˜255 gray levels), and the horizontal axis and the vertical axis respectively represent gray levels and transmittances. Referring to FIG. 1, though the LCD may achieve the wide viewing angle effect according to the aforementioned techniques, in an actual situation, since the side viewing angle gamma curve A is different from the direct viewing angle gamma curve B, when an observer observes an image displayed by the LCD at a relatively large viewing angle (for example 60 degrees), the observed image colour will be different from the image colour observed at a direct viewing angle, and this is the so-called colour washout phenomenon.
To mitigate the colour washout phenomenon appeared under large viewing angle of the LCD, a solution is to divide each of the pixels within the LCD panel into two sub-pixels which may be independently driven, and the transmittance of one of the sub-pixels is constantly greater than that of another sub-pixel, namely, luminance of the sub-pixel with relatively high transmittance is constantly greater than that of the sub-pixel with relatively low transmittance. Therefore, a colour with a middle gray level may be obtained by mixing the colour having relatively high gray level with the colour having relatively low gray level, such that not only the colour washout phenomenon appeared under large viewing angle of the LCD is mitigated, but also similar colour performance of the displayed images may be achieved when the displayed images of the LCD is viewed at the direct viewing angle or the side viewing angle.
However, since one of the sub-pixels is constantly brighter than another sub-pixel, based on such solution, the colour washout phenomenon of the colours with a low gray level and a high gray level may be mitigated perfectly, however, mitigation of the colour washout phenomenon of the colours with a middle and relatively high gray level is limited. Therefore, colour washout phenomenon appeared under large viewing angle of the LCD will still be severe when the displayed images mostly have the colours with the middle and the relatively high gray levels.